There's a festival similar to this around the same time of year called Karneval or Fasnacht which I think has its roots in Roman influence. Did the dressing up on Purim also come from Roman influence or is that just coincidence?
No... The custom of Purim comes from the Holiday itself... Since Hashems miracle was a 'hidden' miracle we dress up in order to express the idea that we are not always what we seem on the outside. Despite external appearances we are Jews... Remember that Purim pre-dates the Roman empire.
http://ohr.edu/yhiy/article.php/1492Here is some info about the customs of Purim {including drinking and costumes}:
http://www.yutorah.org/lectures/lecture.cfm/718099Purim certainly takes it place as one of the more festive holidays of the year. Unlike the other Yom Tov days, the festivities of Purim include certain activities which would normally be frowned upon any other day of the year. This article will discuss some halachic perspectives on those activities.
Drinking on PurimThe Gemara, Megillah 7b, cites the opinion of Rava that one is required to drink wine on Purim until he does not know the difference between the blessings of Mordechai and the curses of Haman. The commentators ask a number of questions regarding Rava's statement. First, the Gemara, immediately after presenting Rava's statement, records an incident where Rabbah became intoxicated on Purim and slaughtered R. Zeira. Rava was a student of Rabbah. Ran, Megillah, 3b s.v. Gemara, quotes Rabbeinu Efraim who asks: how is it possible that Rava would require one to drink wine on Purim if there is even a slight possibility of placing someone's life in danger? Second, getting drunk is an act which is inconsistent with a Torah way of life. Orchot Chaim, Hilchot Megillah UPurim no. 38, asks: how can the rabbis obligate one to commit such an abhorrent act?
Based on these questions, both Rabbeinu Efraim and Orchot Chaim conclude that one should not actually become intoxicated on Purim. Orchot Chaim states that one should drink a little more than he is accustomed to drinking. Many Rishonim seem to subscribe to this opinion and offer various novel interpretations to Rava's statement. [See for example, Rabbeinu Yerucham, Netiv no. 10 and Avudraham, Hilchot Purim.]
R. Moshe Iserles (Rama), Darkei Moshe, Orach Chaim 695:1, cites the opinion of Mahari Brin who suggests that Rambam is also of the opinion that the rabbis did not intend for anyone to become intoxicated on Purim. Rambam, Hilchot Megillah 2:15, states that one should drink wine until he becomes drunk and falls asleep. According to Mahari Brin, Rambam's intention in mentioning falling asleep is to limit the drinking of wine only to the point that one would become sleepy from the consumption of the wine.
Shulchan Aruch, Orach Chaim 695:1, records the statement of Rava. Rama, ad loc., adds that one should not become intoxicated. Rather one should drink more than he is accustomed to drinking and this will cause him to fall asleep. Rama notes that a precondition to any type of drinking is that one should have the noblest intentions. R. Avraham Danzig, Chayei Adam 155:7, rules that if drinking wine will cause one to be negligent in observance of any mitzvah (for example, netilat yadayim, birkat hamazon or tefillah) or to act with frivolity, it is preferable not to enter into that situation. Chayei Adam's statement is codified by Mishna Berurah, Bi'ur Halacha 695:1, s.v. Ad.
Wearing Costumes of Questionable PermissibilityThere is a tradition of wearing costumes on Purim. These costumes can sometimes present halachic problems. Some costumes contain sha'atnez (a prohibited mixture of wool and linen). Others involve the prohibition against a male wearing female garments and vice versa.
R. Yehuda Mintz in his responsa, no. 15, addresses the issue of a male wearing female garments. He notes that according to Tosafot, Avodah Zarah 29a, s.v. HaMistaper, the prohibition against a male wearing female garments only applies if it is for the purpose of beautifying oneself. If the garments are worn for some ulterior motive, there is no prohibition. Therefore, R. Mintz suggests that if a male would like to dress like a female on Purim, it is permissible since his motivation is not to beautify himself, rather to be a part of the festivities.
R. Mintz's ruling is codified by Rama, Orach Chaim 696:8. However, R. Yoel Sirkes, Bach, Yoreh De'ah 182, disagrees. According to Bach, there are two scenarios where it is permissible for a male to wear female garments. First, the prohibition against a male wearing female garments only applies if his intention is to look (at least partially) like a woman. If his intention is anything other than to look like a woman, he may wear female garments. Second, if the article of clothing is one which is not worn for beauty, but rather for protection from the elements, that article may be worn by someone of the opposite gender. Bach claims that dressing like someone of the opposite gender on Purim is not included in either of these leniencies. First, the whole purpose of this act is to look like someone of the opposite gender. Although the original motivation is celebrate Purim, if the means of doing so are through dressing like someone of the opposite gender, it is prohibited. Second, the garments required to dress like someone of the opposite gender are not garments which are worn exclusively to protect one from the elements. Mishna Berurah 696:30, cites the opinion of Bach.
R. Iserles, Darkei Moshe, Orach Chaim 696:5, applies R. Mintz's logic to wearing a costume that contains sha'atnez. The Mishna, K'laim 9:2, states that it is permissible to wear garments containing sha'atnez if one's intention is to avoid taxation on the garment (from someone who is not authorized by the government to collect those taxes). The Gemara, Baba Kamma 113a, states that the reason why there is no violation of the prohibition of sha'atnez is that the prohibition of sha'atnez only applies if one wears the garment for the purpose of wearing it. If one has some ulterior motive in wearing the garment, there is no prohibition. R. Iserles suggests that if one wears a garment containing sha'atnez for the purpose of celebrating Purim and not for the purpose of wearing the garment per se, there is no prohibition. R. Iserles, in his comments on Shulchan Aruch, Orach Chaim 696:8, rules that one may rely on this logic if the costume contains a form of sha'atnez which is only rabbinically prohibited.
Interpersonal MitzvotMordechai, Sukkah no. 743, cites Rabbeinu Shimshon who rules that if there are participants in a wedding who damage the property of other participants as a result of the festivities, they are not required to pay. Sefer HaAgudah, Sukkah no. 41, adds that if a child injures another child while playing in the courtyard of the synagogue, he is not required to pay. Sefer HaAgudah implies that the exemption from liability is based on the idea that when one enters into such a situation, he knows that there may be monetary or physical consequences and he nevertheless chooses to participate. These statements are codified by Rama, Choshen Mishpat 378:9, with the provision that a beit din may institute certain guidelines in order to curb this type of behavior. Rama, Orach Chaim 695:2, adds that if property gets damaged as a result of celebrating Purim, the causer of damage is not liable for the damage.
Rama, Darkei Moshe, Orach Chaim 696:5, cites the opinion of Mahari Brin who notes the practice of some communities that it is acceptable to pilfer small parcels from one another. Mahari Brin notes that he has heard that this practice is cited as justification for wearing costumes of questionable permissibility. He notes that one should reject this justification because the basis for the practice to pilfer on Purim is that in these communities everyone is a willing participant in these "thefts." One cannot extrapolate from this that it is permissible to violate Halacha. While it was already noted that Rama does provide some leniencies regarding wearing costumes of questionable permissibility, Rama (Darkei Moshe) concludes this section with the term (based on a combination of two verses in Tehillim 2:11 and 100:2) "Ivdu et Hashem b'simcha v'gilu bir'ada," one should worship the Almighty with happiness but the rejoice should be tempered with the fear of the Almighty.